|Year : 2014 | Volume
| Issue : 1 | Page : 46-49
Orthodontic extrusion of an impacted tooth with a removable appliance and a bonded attachment: A case report with relevant biomechanics
Pramod Philip1, Ashwin Rao2
1 Department of Orthodontics and Dentofacial Orthopedics, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India
2 Department of Paedodontics and Preventive Dentistry, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India
|Date of Web Publication||21-Jun-2014|
Department of Paedodontics and Preventive Dentistry, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
This case report describes orthodontic extrusion of an impacted central incisor in a 9-year-old child with a removable appliance. Though orthodontic extrusion with removable appliances has been described previously in literature, the aim of this paper is to help the practicing clinician understand the biomechanics and biology of orthodontic extrusion and provide practical tips for using this simple mode of treatment. This will aid the clinician practice orthodontic extrusion in his/her practice in a predictable manner.
Clinical Relevance to Interdisciplinary Dentistry
- The primary aim of this paper is to provide practical tips to the general dentist in carrying out orthodontic extrusion predictably with a simple removable appliance.
- Orthodontic extrusion is indicated in various clinical situations like management of impacted teeth, crown lengthening, treatment of vertical bony defects, etc.
Keywords: Impacted tooth, orthodontic extrusion, removable appliance
|How to cite this article:|
Philip P, Rao A. Orthodontic extrusion of an impacted tooth with a removable appliance and a bonded attachment: A case report with relevant biomechanics. J Interdiscip Dentistry 2014;4:46-9
|How to cite this URL:|
Philip P, Rao A. Orthodontic extrusion of an impacted tooth with a removable appliance and a bonded attachment: A case report with relevant biomechanics. J Interdiscip Dentistry [serial online] 2014 [cited 2019 Sep 20];4:46-9. Available from: http://www.jidonline.com/text.asp?2014/4/1/46/135011
| Introduction|| |
Extrusion is defined as the translation of a tooth along its long axis in a coronal direction. If the movement of the tooth is accelerated by an applied traction it is called orthodontic extrusion. Application of optimal traction forces will lead to a stress distribution all around the periodontal ligament leading to marginal apposition of bone at the alveolar crest. 
Orthodontic extrusion is a relatively common procedure in clinical practice. It is indicated in the following situations:
- Impacted teeth: With the maxillary canine being the most commonly affected tooth
- Traumatically intruded permanent teeth, which needs to be orthodontically repositioned into the occlusal level
- Restorative indications like the management of sub-gingival restorations, tooth fractures at the cervical margin, implant site development etc
- Periodontal indications like management of vertical bony defects.
Orthodontic extrusion can be carried out using fixed or removable appliances. Orthodontic extrusion is discouraging many times for a general practitioner due to inadequate knowledge on the part of the clinician about fixed orthodontic therapy and the biomechanics involved. Insufficient number of teeth could compromise the anchorage, thereby complicating fixed appliance therapy. Though orthodontic extrusion using removable appliances has been previously described in literature,  the aim of this paper is to help understand the biology and biomechanics behind the procedure and aid the general dentist, practice orthodontic extrusion with removable appliances predictably. This case report therefore explains the effective use of a removable appliance in conjunction with a single bonded attachment in the extrusion of an impacted central incisor.
| Case report|| |
A 9-year-old girl was brought to the Department of Pedodontics and Preventive Dentistry by her mother with a chief complaint of an un-erupted upper front permanent tooth. The medical history and the family histories were noncontributory. Extra oral examination revealed nothing significant.
Intra-oral examination revealed the presence of a retained right primary central incisor (tooth no. 51) and a supplementary supernumerary deciduous tooth adjacent to it. An intra-oral peri-apical radiograph revealed the presence of another un-erupted supernumerary tooth and right permanent upper central incisor (tooth no. 11) [Figure 1]a.
|Figure 1: (a) Intra oral periapical: (1) Tooth no. 21, (2) tooth no. 51, (3) tooth no. 52, (4) supplementary supernumerary deciduous tooth, (5) tooth no. 53, (6) tooth no. 11, (7) un-erupted supernumerary tooth, (8) tooth no. 12, (9) tooth no.13, (b) pretreatment intra-oral pictures-right lateral view (c) left lateral view (d) frontal view (e) maxillary occlusal view (f) tomogram showing the mesio-distal and labio-lingual position of the incisor|
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The un-erupted supernumerary tooth was extracted along with the supplemental supernumerary tooth and the retained tooth no. 51 under local anesthesia. The child was put on a monthly recall to check for spontaneous eruption of tooth no. 11.
At 6 months, there was no spontaneous eruption of tooth no. 11. Examination revealed that her right upper premolar had erupted and the left one was erupting. Upper right central incisor was conspicuous by its absence, but the space for the tooth was still intact. The bulge of the crown was palpable clinically [Figure 1]b-d.
A tomogram revealed that the right upper central incisor was present well above the adjacent incisor with around 2-3 mm of soft tissue covering the tooth. It was also evident that the tooth is oriented in the correct labio-lingual inclination [Figure 1]f.
A decision was made to orthodontically extrude tooth no. 11. Though a 2 × 4 appliance was considered, it was not feasible because of insufficient anchorage, as the permanent lateral incisors had not fully erupted into the arch. Hence, it was decided to use a removable appliance for extrusion. The procedure was explained to the child and good cooperation was ensured before attempting the treatment with the removable appliance. Informed consent was obtained from the mother for the same. The extrusion was carried out in the Department of Orthodontics and Dentofacial Orthopedics.
The removable appliance was fabricated with the following design. A full acrylic plate spanning the maxillary arch from the upper incisors to the first permanent molars was made. Adams clasps on first permanent molars and first premolars provided retention of the appliance. A posterior bite-plane was added to the acrylic plate to enhance the stability of the appliance. A hook made with a 0.8 mm stainless steel wire was incorporated into the acrylic plate. The tip of the hook was positioned slightly labial to the center of the arch to ensure that the line of action of the force stays along the long axis. The anterior open bite created by the posterior bite-plane allowed the hook to be positioned well below the occlusal plane creating sufficient stretch of the elastic to provide optimal force levels [Figure 2]a and b.
|Figure 2: (a) Appliance - occlusal view (b) right lateral view (c) schematic diagram explaining the force and the moment generated (d and e) dontrix gauge used for measuring the force level by stretching the elastic to the desired distance|
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The right permanent upper central incisor tooth was surgically exposed and a bracket (Begg bracket) was bonded to the labial surface using light cure composite material. Elastic was stretched between the bracket bonded on the incisor and the hook in the acrylic plate to deliver 20 g of force for the extrusion [Figure 3]a. The elastic was chosen after measuring the force with a dontrix gauge [Figure 2]d and e.
The child was instructed to wear the appliance throughout the day except during eating. The elastic was changed once a day. The active treatment continued for a period of 4 months, following which the child wore the appliance for another 2 months with a minimal force of 5 g to retain the tooth in the extruded position [Figure 3]b.
|Figure 3: (a) Appliance in the mouth with elastic applied between the bonded bracket and hook (b) posttreatment intra-oral frontal photograph|
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The vertical position of the lower incisors was carefully monitored during the whole treatment period to ensure that there is no supra-eruption.
| Discussion|| |
Orthodontic extrusion has become a very common clinical procedure with various indications. A clinician who is attempting the same should have adequate understanding of the biological and the biomechanical aspects of the procedure.
Biology of orthodontic extrusion
Application of light forces lead to coronal migration of the root along with the bony ridge leading to an increase in the attached gingiva. The increase in the attached gingiva is initially seen as an eversion of sulcular epithelium which is nonkeratinized. It gets keratinized over a period of 28-42 days. , The extrusion leads to bone deposition at the root apex as well as the alveolar crest of the extruded tooth and a normal relationship will be maintained between the alveolar crest and the cement-enamel junction if the periodontium is healthy.  The gingival tissue, which moves coronally needs to be surgically excised for optimal esthetics (as in the case of anterior teeth) or for the placement of proper margin of the restorations. Some researchers recommend the weekly excision of the supra-crestal fibers where as others recommend a single excision at the end of the whole procedure depending on the amount of fibrotomy required.  A light continuous force is desirable for the remodeling of the periodontal tissue and subsequent bony deposition with in the alveolar socket.
Rapid extrusion with the application of heavy forces will result in a less pronounced migration of supporting tissue as the tooth tends to move faster than the rate of physiologic adaptation of the soft tissue. Hence it requires an extended period of retention to allow the investing tissues to adapt to the new position of the tooth. There is a risk of periodontal tear and resultant ankylosis of the tooth.  Heavy forces can also lead to external root resorption.
Care should be taken to have minimal exposure of the tooth surface for the purpose of bonding an attachment.  As the crown bulge was visible through the gingiva, a small window was created for the purpose of bonding the bracket.
Optimal force needed for orthodontic extrusion
Optimal force for the forceful extrusion depends on the tooth involved and it can vary from 15 g for a lower incisor to 60 g for a molar. The applied force should be based on the physiologic response of the individual tooth depending on its root size, root length root morphology and the periodontal support. It should also be based on the rate of tooth movement in individual cases. A rate of 1 mm of extrusion per week is considered physiologic for slow extrusion. ,
In the present case, a force of 20 g was applied and the tooth moved at a very slow rate of 1.5 mm/month. This could be attributed to the presence of scar tissue formed secondary to the surgical extraction of supernumerary tooth. As the tooth was an immature permanent tooth, it was decided to keep the force levels minimum enough to bring about extrusion without undue damage to the root and the investing tissues.
Extrusion can be achieved by the application of a single force with a point contact of application delivered from an appropriate anchorage unit with a desired line of action. The biomechanics of extrusion varies with the design of the appliance used. Care should be taken to minimize the effects of reactionary forces on the anchorage unit. If fixed appliance is used for extrusion, addition of a sufficient number of teeth in the anchorage unit prevents the reciprocal effects on the anchor unit.
A removable appliance usually provides anchorage from the palate. Retention of the appliance in the mouth is more critical in case of a removable appliance as the reciprocal force tends to dislodge the appliance from the mouth. Properly designed appliance with adequate retentive clasps ensures the stability of the appliance in the mouth when traction is applied for orthodontic extrusion.
The applied force creates a clockwise moment which tends to rotate the tooth. The moment is created because the point of force application of force (elastic is applied to the bracket) is away from the center of resistance (as shown by a dot in the root) of the tooth. The force extrudes the tooth while the moment brings about a lingual tipping [Figure 2]c.
Stability of the procedure
Questions are raised regarding the stability when the extrusions are carried out at a very rapid rate. That is attributed to a lag in the coronal migration of the tissue as against the pace at which the tooth has moved. Mostly, orthodontic extrusion is carried out over a period of 4-6 weeks with 1 mm of tooth movement per week. This is followed by a stabilization period of 6-8 weeks during which the remodeling of the supporting structures occur. Prolonged retention for a period of 6 months is recommended by some researchers in cases of the implant site development as the quality and the density of the bone formed improves with such a prolonged period of retention. ,
The incisor in the present case was brought down at a very slow rate of 1.5 mm/month and retained for an additional period of 2 months with the help of elastics. Clinical examination at that time revealed that the patient presented with a mild bi-maxillary dento-alveolar proclination which might require a fixed appliance therapy at an appropriate time because of which the final leveling of the four incisors was not attempted.
Certain clinical guidelines need to be followed while attempting orthodontic extrusion with a removable appliance:
- Ensure adequate patient compliance
- The periodontal status and the quality and the quantity of the attached gingiva to be evaluated carefully
- The design of the appliance should be contusive for optimal biomechanics and good retention of the appliance
- The area of surgical exposure should be kept to the bare minimum to bond an attachment
- The force applied should be light and continuous in nature and should bring about frontal resorption
- Adequate period of retention should be provided to prevent any relapse.
| Conclusion|| |
Orthodontic extrusion is commonly carried out by trained specialists. A simple removable appliance along with a bonded attachment has been used successfully in this case to bring about the required extrusion. This should encourage more general practitioners to attempt an orthodontic extrusion with a removable appliance therapy.
| References|| |
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[Figure 1], [Figure 2], [Figure 3]